A nutritional retinal degeneration of cats, resulting in atrophy of photoreceptor outer segments, has been induced by dietary means in as little as 6 weeks by restricting the protein concentration of the diet in kittens and adults. It is the objective of the proposed research to determine whether protein per se, or some factor related to protein, is the basis of the deficiency and to determine how this factor is required by the retina for normal vision. The basic protein requirements for growth and vision will be estimated in a series of nutritional studies that will include varying the quality and quantity of protein and eventually feeding specific supplements of the identified component (amino acid?) to attempt to avert the blindness. Stages of blindness will be monitored with electroretinography and electron microscopy and the progression of the lesion mapped histologically. Once the deficient factor is identified, it is anticipated that a tritiated label can be obtained which will be injected and localized in the retina by autoradiography to determine where and how the nutrient is incorporated into the retina and changes in retinal metabolism induced by the deficiency.